Real-world analysis of ctDNA and other biomarkers in patients with curatively resected stage I-III biliary tract cancer.

4130 Background: Growing evidence supports the prognostic and predictive value of circulating tumor DNA (ctDNA) detection in gastrointestinal cancers. Building on previous work that demonstrated the feasibility of tumor-informed ctDNA testing in biliary tract cancer (BTC), this study aimed to evaluate ctDNA as a tool for detecting molecular residual disease (MRD) following curative resection and monitor recurrence during surveillance. Methods: A retrospective analysis of real-world data was performed on patients (N=171) with stage I-III resectable BTC who underwent ctDNA analysis using a personalized, tumor-informed 16-plex mPCR-NGS assay (Signatera; Natera, Inc.) from July 2020-February 2024. Plasma samples (n=769) were collected pre-operatively, postsurgically (within 2 to 12-weeks; MRD window), and longitudinally until death or last follow-up (surveillance window). The prognostic value of ctDNA was compared to traditional biomarkers such as CA19-9 and CEA. Results: A total of 171 patients with stage I-III BTC with a median age of 68 years (range 27-92) were included in this analysis. The median follow-up was 21 months (range: 2-97 months). ctDNA detection rates during the MRD and surveillance windows were 22% (18/83) and 32% (35/109), respectively. On evaluating clinical outcomes, ctDNA-positivity during MRD and surveillance was significantly associated with inferior disease-free survival (DFS) and overall survival (OS). Multivariate analysis confirmed ctDNA-positivity to be the most significant prognostic factor associated with DFS (HR: 10.91, 95%CI: 3.85-30.9, P<0.001) when adjusted for other clinicopathologic factors such as BTC subtype or tumor grade. Additionally, other biomarkers such as CA 19-9 and CEA did not predict clinical outcomes at either the MRD or surveillance windows (Table). Conclusions: The data show that ctDNA-positivity was associated with poor DFS and OS, both in the post-op and surveillance settings and that ctDNA detection using a personalized, mPCR-NGS assay was superior to current clinical biomarkers. These findings highlight the value of ctDNA monitoring to improve prognostication in BTC. Association of biomarkers with clinical outcomes. Biomarker MRD Surveillance ctDNADFS OS n= 83HR: 13.0, p < 0.001HR: 12.0, p < 0.001 n= 109HR: 6.1, p < 0.001HR: 17.8, p = 0.008 CA19-9DFSOS n= 53HR: 0.88, p =0.81HR: 1.9, p = 0.389 n= 80HR: 1.3, p = 0.51HR: 10.1, p = 0.045 CEADFSOS n= 18HR: 0.84, p = 0.85HR: 1.7, p = 0.71 n= 18HR: 0.54, p = 0.5HR: Not evaluable